Anderson.] 



Point Reyes Peninsula. 



135 



ward. At the western end of the ridge, below the light-keepers' 

 dwellings, and along the shore both at the south and west for a 

 short distance, the conglomerates have a thickness of at least three 

 hundred feet. The dip here is generally about 35 toward the 

 west, though some of it is steeper. 



The conglomerates here are not of uniform composition, but are 

 made up of large boulders, cobblestones, pebbles, and sand that 

 are very irregularly distributed. The basal portion of the series is 

 somewhat distinct from these conglomerates, although it is appar- 

 ently conformable with them. It consists of a dark sandy shale, 

 about fifty or sixty feet in thickness, that holds its position pretty 

 constantly throughout the whole length of the ridge. It contains a 

 few layers of a calcareous concretionary material, in which search 

 was made for fossils, though without success. This shale rests 

 directly upon the granite, and is overlain above by massive beds of 

 conglomerate. It seemed a little surprising that it should be found 

 in this position, and at first suggested an earlier age, but its regularity 

 and comformability below the conglomerates indicate that it marks 

 only a change of conditions while yet below water level. The 

 conglomerates are evidently shore deposits, while the shales are 

 probably not. 



The heaviest boulders that were seen in these conglomerates are 

 in their upper portions near the lighthouse, where some of them 

 measure four or five feet in length. There is no ready explanation 

 of this fact, unless we suppose that the changes connected with the 

 formation of these conglomerates were progressive, and in their 

 later stages moved the shore-line only a little farther seaward, thus 

 depositing heavier material upon that which had previously been 

 formed farther from shore. Along the shore of Drake's Bay, where 

 the granite crops out on the beach, the conglomerates are less than 

 one hundred feet in thickness, and rest directly upon the granite, 

 without the occurrence of the shales that intervene at other points 

 along the ridge. The stones and pebbles of these conglomerates 

 are mainly of granite and quartzite, with an occasional representa- 

 tive of a hard, dark, porphyritic rock and a little slate. 



Succeeding the conglomerates at all the localities mentioned, are 

 thick beds of sandstone of a light yellowish color. They are 



2 



